As physical quantity sensors outputting a signal corresponding to angular velocity or acceleration applied to apparatuses, there are known angular velocity sensors detecting the angular velocity applied to the apparatuses, acceleration sensors detecting acceleration of dropping velocity or the like, gyro sensors measuring angular velocity (rate gyros) and an angle (posture gyros), and the like. In a case where those physical sensors are installed in a vehicle and the like, and utilized as a crash sensor, it is fatal that a crash cannot be detected due to failures in the sensor.
In order to solve this problem, for example, Patent Document 1 shows a method in which, in a rotational velocity sensor having a detection arm vibrated in accordance with rotation, a testing electrode is fixed to the detection arm so as to be electrostatically coupled with the arm, and the detection arm is vibrated as a test by a testing signal supplied from the testing electrode before starting.
[Patent Document 1] Japanese Patent No. 2935810.
The conventional method, however, sacrifices the sensitivity of the rotational velocity sensor due to the testing electrode attached to the detection arm, and further has a problem in that the increased number of electrical contacts due to the testing electrode added to electrodes normally used impairs the reliability.